1. Field of the Invention
The present invention relates to a method of producing a polymerized toner (hereinafter, it may be simply referred as “a toner”) used for development of a latent image of electrostatics in an electrophotography, an electrostatic recording method and an electrostatic printing process or the like. Particularly, the present invention relates to a method of producing a polymerized toner which is high dewatering efficiency and drying efficiency and is excellent in productivity.
2. Description of the Related Art
A method of producing a colored resin particle which is a main component of the toner is classified into a dry method and a wet method. As the dry method, there may be a pulverization method or the like, which is a method of producing the colored resin particle by melting and kneading a binder resin with a colorant and other additives or the like, and then pulverizing and classifying it. In contrast, as the wet method, there may be a polymerization method, a solution suspension method or the like, which is a method of producing the colored resin particle in an aqueous dispersion medium.
A form of the colored resin particle obtained by the pulverization method is an indeterminate, whereas a form of the colored resin particle obtained by the wet method such as the polymerization method and the solution suspension method is close to spherical form and has a small particle diameter and narrow particle size distribution.
Among the wet methods, by the polymerization method, a polymerized toner having easily-controlled particle diameter, spherical form with a small particle diameter and narrow particle diameter distribution can be produced.
Recently, an attempt to further minimize the particle size of the toner is made with the further rise in the demand level to an image printing having high resolution and high quality. Even the polymerized toner, new problems have been pointed out.
As the above-mentioned problems, in the polymerization step of producing the polymerized toner, it is pointed out to have an adverse affect on the productivity of the toner and a printing ability by producing a particle having unnecessary microparticle diameter as a by-product other than desired colored resin particle.
A minute by-product particle of the majority is a microparticle having less than 0.6 μm of particle diameter, so called, submicron order and not containing the colorant (hereinafter, it may be referred as “a by-product microparticle”).
If such the by-product microparticle is produced as a by-product, a part of released by-product microparticle clogs the filter upon filtration of the obtained colored resin particle from the aqueous dispersion medium and a filtration rate decreases, thereby causing a decrease in a production efficiency of the toner. Also, if the polymerized toner containing a lot of by-product microparticles is used for image-forming, the by-product microparticle is likely adhere to members in a developer upon printing. When plural prints are printed, the attached by-product microparticle is gradually accumulated so as to cause adherence to the member, thus it is known to have an adverse affect on the printing ability of the toner.
To obtain the polymerized toner, in addition to need to remove the by-product microparticle which is produced as a by-product upon polymerization, it is also necessary to dry the wet colored resin particle (wet cake) which is obtained by carrying out solid-liquid separation of the colored resin particle from the aqueous dispersion of the colored resin particle and the washing and dewatering process. When the wet cake after the washing and dewatering process is dried, if water is not sufficiently-removed and dried, it takes much time to dry thereof, thus drying efficiency is decreased and a problem to be declined a productivity of the toner is occurred.
The applicant have been continued to make an attempt to improve efficiency of the steps such as the solid-liquid separation (filtration), washing and dewatering in order to efficiently obtain desired colored resin particle without deteriorating a quality of the colored resin particle.
JP Patent Application Laid-open (JP-A) No. H8-160661 discloses the method of producing the polymerized toner by carrying out the solid-liquid separation, washing and dewatering by the use of continuous belt filter, Siphon Peeler Centrifuge, or both of them as a washing dehydrator.
JP Patent Application Laid-open (JP-A) No. 2004-302099 discloses the method of producing the polymerized toner by efficiently carrying out a vacuum deliquoring of a cake by giving an oscillation or an impact to a cake layer formed on a filter fabric at a part of the vacuum deliquoring zone of the vacuum belt filter in the step of filtering and washing by the use of the vacuum belt filter.
Further, JP Patent Application Laid-open (JP-A) No. 2004-302098 discloses the method of producing the polymerized toner in the step of filtering and washing by the use of a vacuum belt filter by bringing a filtrate in a gravity-settling zone and a filtrate in a cake forming zone back on a cake of a vacuum filtrating zone, peeling the cake and using a washing drainage which washes the filter fabric as a wash solution.
Further, JP Patent Application Laid-open (JP-A) No. 2003-275514 discloses the method of producing the polymerized toner by using a horizontal belt vacuum filtration apparatus provided with a filter element whose lengthwise tension strength is 200 kgf/30 mm or more, a ventilation volume is preferably 150 cc/min/cm2 or less upon separation of the colored resin particle from the dispersion of the colored resin particle.
However, a method of producing the toner whose process is provided with a step of removing the by-product microparticle generated as a by-product upon polymerization from the colored resin particle, which controls the state of the dispersion of the colored resin particle in the solid-liquid separation (filtration) and the washing and dewatering of the process of producing the toner, and which has an excellent productivity and printing ability has not been attained.